The mechanisms of summer dryness induced by greenhouse warming
- Princeton Univ., NJ (United States)
To improve understanding of the mechanisms responsible for CO{sub 2}-induced, midcontinental summer dryness, several integrations were performed using a GCM with idealized geography. The simulated reduction of soil moisture in middle latitudes begins in late spring, caused by excess of evaporation over precipitation. Increase of carbon dioxide and the associated increase of atmospheric water vapor enhances the downward flux of terrestrial radiation at the continental surface at all latitudes. However, the increase in the downward flux of terrestrial radiation is larger in the equatorward side of the rain belt, making more energy available there for both sensible and latent heat. Evaporation increases more than precipitation over the land surface in the equatorward side of the rain belt during spring and early summer and initiates the drying of the soil there. As the rain belt moves poleward from spring to summer, the soil moisture decreases in middle latitudes, reducing the rate of evaporation. This reduction of evaporation, in turn, causes a corresponding decrease of precipitation in middle latitudes, keeping the soil dry throughout the summer. In high latitudes, there is also a tendency for increased summer dryness. Earlier removal of highly reflective snow cover in spring enhances the evaporation in the late spring, lengthening the period of drying during the summer season. The drying of soil is also enhanced by the land surface-cloud interaction. Solar radiation absorbed by the continental surface increases, enhancing evaporation and further reducing the soil moisture in summer. A greater fraction of radiative energy occurs as sensible heat rather than latent heat due to the colder surface temperature, causing evaporation to increase less than precipitation. Because of increased evaporation from the oceanic surface upstream, precipitation over most of the continent increases substantially.
- OSTI ID:
- 255675
- Journal Information:
- Journal of Climate, Journal Name: Journal of Climate Journal Issue: 12 Vol. 8; ISSN JLCLEL; ISSN 0894-8755
- Country of Publication:
- United States
- Language:
- English
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